A growing risk of asymmetric attacks has increased the need for distributed chemical detectors or detectors for other agents with vastly superior false positive rates relative to current solutions. Using two tiered sensors for detecting biological or other hazards are known. However, these known arrangement of two tiered sensors typically consist of two types of sensors that are co-located at a sensor location such that the more sensitive or more reliable sensor is only operated or triggered when the less sensitive or less reliable sensor initially detects a presence of an agent that is being monitored.
However, in view of the risks posed by terrorism, some of the chemical warfare and other toxic agents need to be monitored over a vast area. Use of such known co-located dual sensors may be prohibitively expensive if used to cover such a vast area that needs to be monitored.